You would have to discuss what level of riders will be riding him in the lessons and how frequent he would be used. He's your horse and you know him best, that said if he was to be used for a bunch of beginner he may or may not be the same after a year of a bunch of new riders pulling on his mouth and giving wrong cues vs just one person leasing him.
As for leasing to 1 person, you can pick who rides him and find him a good match. Someone who will ride him and care for him as you do. And if it doesnt work out or you find that they are not giving him the best care you can always cancel the agreement.
Make sure everything is in writing concerning who rides him and when/how much, where he will be kept, who will care for him, who pays for feed, trimming, board, any emergency vet bills, etc and be very detailed. Make sure it is also in writing that at any time you feel your horse is not meeting expectations of care you can cancel the agreement. Etc There are others on here that know more about lease agreements.
I personally would just keep him if money wasnt an issue. Most horses will be fine with a year off in the pasture, and you could do a bunch of ground work with him (teach him some tricks) and strengthen your bond while you are at it and not risk anyone else ruining your training on him.